In the United States, premature birth is the most prevalent cause of infant morbidity and mortality in nonanomalous newborns. Approximately 10 percent of all pregnancies results in preterm delivery and this rate has increased in recent years. In a large majority of preterm births the etiology is unknown. Environmental stress identified as factor that may contribute these adverse outcomes because it has been linked to shorter gestations. It is proposed here that the timing of environmental perturbations is important in determining their because maternal sensitivity to the environment during pregnancy is dynamic. Preliminary evidence suggests that the impact of the environment, on both maternal responses and birth outcome, decreases as pregnancy advances. The main objective of this proposal is to assess the effects of advancing pregnancy on maternal sensitivity to the environment. The project will, for the first time, characterize these changes longitudinally in a single sample of women. This proposal will assess changes in physiological, psychological, cognitive and sensory systems during pregnancy, determine how the breadth and magnitude of these changes are associated with birth outcome and relate these changes to the products of the hypothalamic-pituitary-adrenal-placental axis. The project includes three specific aims: 1) Characterize the effects of pregnancy on environmental sensitivity. We will measure changes in cardiovascular reactivity, anxiety and stress responses, memory and tactile sensitivity repeatedly during gestation. As pregnancy advances, it is expected that there will be declines in physiological, psychological and cognitive responding. 2) Determine how birth outcomes are influenced by changes in environmental sensitivity. It is anticipated that women who show the smallest decreases in sensitivity will be more likely to deliver infants of younger gestational age and that those women who show the largest decreases in sensitivity will be more likely to deliver at term because it is believed that these decreases are protective. 3) Assess the association between changes in environmental sensitivity and the products of the hypothalamic-pituitary-adrenal-placental axis. During the course of this study data will be collected from 200 pregnant women (half Hispanic and half non-Hispanic whites) three times during pregnancy and once post-partum. At each study visit, cardiovascular reactivity, emotional state, memory, tactile sensitivity and neurohormonal levels will be assessed. This project is designed to characterize the decrease in maternal sensitivity to environmental pertubations during pregnancy and will provide new insight into the potential of the environment to affect adverse pregnancy outcome.